Mole Calculations & Equations

Ogjectives: be able to relate number of grams, number of moles and number of molecules for a substance; Balance equations & perform mole calculations

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What is the formula mass of H2O?

18.02 amu

What is the formula mass of (NH4)2SO4?
132.17 amu

How many molecules are contained in 1.00 mole of carbon dioxide? How many atoms?

6.02 x 1023 molecules, 1.81 x 1024 atoms

Balance the equation: SO2 + O2 ---> SO3

2SO2 + O2 ---> 2SO3

For the reaction in the preceding question, how many moles of sulfur trioxide would be formed if 5.0 moles of oxygen is consumed in the reaction?

10 moles

Balance the equation: C4H10 + 02 ---> CO2 + H2O

2C4H10 + 13O2 ---> 8CO2 + 10H2O

Atoms are neither created nor destroyed in an ordinary chemical reaction. True or False

True

The mass of a mole of a substance depends on the identity of the substance. True or False

True

In a balanced chemical equation there must be the same total number of molecules on each side of the equation. True or False

False

In balancing an equation formula subscripts are adjusted as needed to obtain the balance. True or False

False

A mole of HF weighs the same amount as a mole of HCl. True or False

False

What is the weight (in grams) of one mole of:

Cu atoms

LiBr

(NH4)2SO4

63.55 g, 86.84 g, 132.17 g

How many molecules are in 3.60 moles of NH3? How many moles of H atoms?

3.60 moles * 6.02 x 1023 molecules/mole = 21.7 x 1023 = 2.17 x 1024 molecules * 3 H atoms / molecule = 6.51 x 1024 atoms

How many moles are contained in 75.0g of CaCO3?

75.0 g * 1 mol / 100.09 g = 0.749 moles

For the reaction: 2 Mg + O2 --> 2MgO , how many moles of product will be formed if 2.25 moles Mg are reacted with excess bromine?

2.25 mol Mg * 2MgO / 2Mg = 2.25 moles MgBr

In the reaction 2 HgO --> 2Hg + O2, 50.0g of mercury is formed. How many grams of HgO were used in this reaction?

First find the number of moles of product formed: 50.0g Hg * 1 mol / 200.59g = 0.249 moles Hg (more)

How many moles of reactant were used? 0.249 moles Hg * 2HgO / 2 Hg = 0.249 moles HgO used (more)

How many grams would this be? 0.249 moles HgO * 216.59g / mol HgO = 53.9g HgO

A 52.5 gram sample of silver nitrate reacts with calcium chloride to yield silver chloride and calcium nitrate. How many grams of silver chloride will be produced?

First a balanced equation: 2 AgNO3 + CaCl2 ---> 2 AgCl + Ca(NO3)2 (more)

How many grams were reacted? 52.5 g * 1 mol/169.88 g = 0.309 moles AgNO3 (more)

How much product? 0.309 moles AgNO3 * 2 moles AgCl / 2 mole AgNO3 = 0.309 moles AgCl * 143.32 g / mol = 44.29 g AgCl